The present invention relates to synthetic based lubricants which are particularly useful for lubricating heavy duty diesel engines.
Specifications for modern engine lubricants, such as those for heavy duty diesel engines, especially in Europe, indicate a longer interval between oil changes than has been customary in the past. In order to formulate engine oils with longer drain intervals, higher levels of certain additives have been incorported, typically greater than 1.7% by weight detergent substrate and greater than 10 TBN (Total Base Number, ASTM D2896) in the finished lubricant. Additionally, synthetic base stocks have been used to improve the thermo-oxidative stability of the base oils. These high levels of detergent soap substrate and TBN provide improved piston cleanliness and reduced engine wear over drain intervals which may be in excess of 100,000 km. However, the high level of detergent can cause higher levels of valve train wear, as measured in the Cummins M11 valve train wear test.
To address the problem of increased valve train wear, a heavy duty diesel lubricant has now been formulated using a selection of synthetic base oils, a dispersant-viscosity modifier, and a sulfur-free functionalized alkyl phenol detergent. The preferred lubricant also exhibits good emissions performance.
U.S. Pat. No. 5,719,107, Outten et al., Feb. 17, 1998, discloses a crankcase lubricant for diesel engines, comprising an admixture of a major amount of an oil of lubricating viscosity, at least 4 mass % dispersant, at least 0.3 mass % of a metal phenate, which may be neutral or overbased, and various other components. The oil can be any of the synthetic or natural oils, or mixtures. The oil has a viscosity of about 2.5 to about 12 mm.sup.2 /sec. Multifunctional viscosity modifiers that also function as dispersants are also disclosed. Suitable metal phenates include calcium, magnesium, and mixtures of the two.
U.S. Pat. No. 2,647,873, Matthews et al., Aug. 4, 1953. discloses compounds which are suitable as additional agents to lubricating oils and greases. Metal salts and condensates are prepared from the following ingredients: an aromatic compound containing a polar radical or radicals (e.g., phenols), and aldehydes such as formaldehyde. The Ca, Mg, Sr, Cu, Zn, Al, and Sn salts of certain of these condensation products are disclosed.